Gelation of gellan – A review

In situ-forming hydrogels for sustained ophthalmic drug delivery.

Aerobic sludge granulation: A tale of two polysaccharides?

Rheological and thermal studies of gel-sol transition in gellan gum aqueous solutions

Gelation kinetics, mechanical spectra, thermal scanning rheology (TSR), and differential scanning calorimetry (DSC) in aqueous solutions of gelling polymers and colloids such as seaweed polysaccharides (agarose, carrageenans), microbial polysaccharides (gellan, curdlan), plant polysaccharides (methylcellulose), globular proteins (casein, glycinin, β-conglycinin), fibrous proteins (gelatin, fibrin), and polyvinyl alcohol, which are related to foods, cosmetics, biomedical and pharmaceutical applications, are described. Some gelation processes at a constant temperature have been treated successfully by an equation of first order kinetics or by other modified equations, and the molecular mechanism of gel formation is discussed briefly. For water-soluble polymers, the criterion of the gel or sol based on the frequency dependence of storage and loss moduli gives valuable informations. TSR and DSC are complementary, and the combination of these methods has been proved to be useful.

Rheological and DSC study of sol-gel transition in aqueous dispersions of industrially important polymers and colloids

Publisher Summary Following the spectacular commercial success of their first bacterial polysaccharide xanthan, Kelco (now a Division of Merck) has developed three new commercial polymers from microbial fermentation—namely, gellan, welan, and rhamsan. This chapter presents a study that explores the relationships between the primary structure, conformation, and physical properties of these materials. Gellan gum is a deacylated form of the extracellular bacterial polysaccharide from Auromonas elodea (ATCC 31461). In the native form, it has an L-glyceryl substituent on O-2 of the 3-linked glucose and an acetyl group on approximately half of the O-6 atoms of the same residue, but both these groups are lost during normal commercial extraction. Welan, from Alcaligenes ATCC 31555 (formerly known as S-130), has the same backbone sequence as gellan, but with a monosaccharide side chain at O-3 of the 4-linked glucose; this can be either α-L-rhamnose or a-L-mannose, in the approximate ratio 2:1. Welan does not gel, but forms viscous solutions that can suspend particles or stabilize emulsions in a manner similar to xanthan “weak gels.” These properties are stable to high temperatures and the polymer is intended primarily for commercial use in oil recovery. Rhamsan, the exopolysaccharide from Alcaligenes ATCC 31961 (formerly known as S-194), is also a branched variant of gellan.

Geoffrey Robinson

Papers

Conformation and Physical Properties of the Bacterial Polysaccharides Gellan, Welan, and Rhamsan